It is already known from U.S. Pat. No. 5,099,246 to determine the roll angle position with the aid of polarised electromagnetic radiation, comprising a transmitter arranged to emit a polarized radiation in the direction towards the projectile and a polarization-sensitive receiver arranged in the projectile. By having the emitted polarized radiation consisting of at least two mutually phase-locked radiation components with a wavelength ratio of 2:1 and/or multiples thereof, which are superposed and form an asymmetrical curve shape, the roll position of the projectile can be unambiguously determined.
In abovementioned apparatus that a transmitter is placed in connection with the launching position of the projectile and the projectile is provided with a rearward-directed receiving antenna in order to receive the transmitted radiation.
Although an apparatus of the type described permits an unequivocal determination of the roll position with satisfactory precision and without ambiguity, it can be a disadvantage to be dependent on two mutually phase-locked frequencies since both the transmitter and receiver become more complicated.
It is also already known to determine the roll angle position by magnetic means by sensing the earth's magnetic field, see EP 0 319 649. Such a system is, however, latitude-dependent and sensitive, to interference.